Today, two types of image scanning devices are commonly available for converting paper documents into electronic images. The first type is a flatbed scanner, which scans document placed on a flat transparent glass or plastic window. The second type is a sheet-feed scanner, which feeds pages of documents, one page at a time, through a thin slot on the scanner to be scanned. Currently, the image scan speed of sheet-feed scanners is usually much faster than that of the flatbed scanners. In flatbed scanners, one critical limiting factor for scan speed is the mechanical movement speed of the scan head in the scanner. A fast back and forth and start-and-stop movement of the scan head can create a level of vibration that hurts the image quality of the flatbed scanner. Alternative to scan head, a rotatable mirror may work as a scan mechanism in a flatbed scanner.
The reduction of the vertical dimension of flatbed scanner while keep a large scan area, so that the scanner has a “thin” physical profile is very important for the flatbed scanner as a commercial product. One way of addressing this problem is to use multiple rotatable mirrors, each scanning a different region of the scan area to achieve a “thin” scanner design. This method is described in U.S. application Ser. No. 10/960,791.
It is desirable to use fewer rotatable mirrors, preferably one rotatable mirror, for simple mechanism structure and low cost of the flatbed scanner.
The current invention provides a solution to use fewer rotatable mirrors, preferably one, in flatbed scanner design.